Computer simulation of a CF(4) plasma etching silicon. II. Sensitivity analysis.

Sensitivity analysis applied to reaction kinetics is being increasingly recognized as a powerful tool for identifying the controlling steps in a complex mechanism. This analysis can be used to improve a simulation by indicating areas where further refinement will be most effective. The technique has been applied to model silicon etching by a carbon tetrafluoride (CF(4)) plasma. It is shown that gas phase composition is dominated by the chemistry of neutral species and that the plasma serves mainly as a source of active radicals. Recombination of these radicals occurs mostly on the walls. This wall recombination provides an alternate path to final products which competes with the etching process for active species. Thus it is concluded that a better description of transport and surface reactions is crucial to the correct modeling of the system, and that advances in this area are of highest priority for a better under- standing of the etching process.